import java.util.LinkedList;
import java.util.Queue;

class MyStackUse {

    public Queue<Integer> qu1;
    public Queue<Integer> qu2;

    public MyStackUse() {
        qu1=new LinkedList<>();
        qu2=new LinkedList<>();
    }
    
    public void push(int x) {
        if (!qu1.isEmpty()){
            qu1.offer(x);
        } else if (!qu2.isEmpty()) {
            qu2.offer(x);
        }else {
            qu1.offer(x);
        }
    }
    
    public int pop() {
        if (empty()){
            return -1;
        }
        if(!qu1.isEmpty()){
            int size=qu1.size();
            for (int i = 0; i < size-1; i++) {
                qu2.offer(qu1.poll());
            }
            return qu1.poll();
        } else{
            int size=qu2.size();
            for (int i = 0; i < size-1; i++) {
                qu1.offer(qu2.poll());
            }
            return qu2.poll();
        }

    }
    
    public int top() {
        if (empty()){
            return -1;
        }if(!qu1.isEmpty()){
            int size=qu1.size();
            int val=0;
            for (int i = 0; i < size; i++) {
                val=qu1.poll();
                qu2.offer(val);
            }
            return val;
        } else{
            int size=qu2.size();
            int val=0;
            for (int i = 0; i < size; i++) {
                val=qu2.poll();
                qu1.offer(val);

            }
            return val;
        }
        
    }
    
    public boolean empty() {
        return qu1.isEmpty()&&qu2.isEmpty();
    }
}